440 research outputs found
Synthesis of the Einstein-Podolsky-Rosen entanglement in a sequence of two single-mode squeezers
Synthesis of the Einstein-Podolsky-Rosen entangled state --- the primary
entangled resource in continuous-variable quantum-optical information
processing --- is a technological challenge of great importance. Here we
propose and implement a new scheme of generating this state. Two nonlinear
optical crystals, positioned back-to-back in the waist of a pump beam, function
as single-pass degenerate optical parametric amplifiers and produce single-mode
squeezed vacuum states in orthogonal polarization modes, but in the same
spatiotemporal mode. A subsequent pair of waveplates acts as a beam splitter,
entangling the two polarization modes to generate the Einstein-Podolsky-Rosen
state. This technique takes advantage of the strong nonlinearity associated
with type-I phase-matching configuration while at the same time eliminating the
need for actively stabilizing the optical phase between the two squeezers,
which typically arises if these squeezers are spatially separated. We
demonstrate our method in an experiment, preparing a 1.4 dB two-mode squeezed
state and characterizing it via two-mode homodyne tomography.Comment: 4 pages, 3 figure
Acoustic Properties of Porous Coatings for Hypersonic Boundary-Layer Control
Numerical simulations are performed to investigate the interaction of acoustic waves with an array of equally
spaced two-dimensional microcavities on an otherwise flat plate without external boundary-layer flow. This acoustic
scattering problem is important in the design of ultrasonic absorptive coatings for hypersonic laminar flow control.
The reflection coefficient, characterizing the ratio of the reflected wave amplitude to the incident wave amplitude, is
computed as a function of the acoustic wave frequency and angle of incidence, for coatings of different porosities, at
various acoustic Reynolds numbers relevant to hypersonic flight. Overall, the numerical results validate predictions
from existing theoretical modeling. In general, the amplitude of the reflection coefficient has local minima at some
specific frequencies. A simple model to predict these frequencies is presented. The simulations also highlight the
presence of resonant acoustic modes caused by coupling of small-scale scattered waves near the coating surface.
Finally, the cavity depth and the porosity are identified as the most important parameters for coating design.
Guidelines for the choice of these parameters are suggested
Alternate Designs of Ultrasonic Absorptive Coatings for Hypersonic Boundary Layer Control
Numerical simulations of the linear and nonlinear two-dimensional Navier-Stokes equations are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings consisting of a uniform array of rectangular pores (slots) with a range of porosities and pore aspect ratios. Based on our previous work, we employ a temporally evolving approximation appropriate to slowly-growing second-mode instabilities. We consider coatings operating in attenuative regimes where the pores are relatively deep and acoustic waves and second mode instabilities are attenuated by viscous effects inside the pores, as well as cancellation/reinforcement regimes with alternating regions of local minima and maxima of the coating acoustic absorption, depending on the frequency of the acoustic waves. The focus is on reinforcement cases which represent a worst case scenario (minimal second-mode damping). For all but one of the cases considered, the linear simulations confirm the results of linear instability theory that employs an approximate porous-wall boundary condition. A particular case with a relatively shallow cavities and very high porosity showed the existence of a shorter wavelength instability that is not predicted by theory. Finally, nonlinear simulations of the same cases led to the same conclusions as linear analysis; in particular, we did not observe any "tripping" of the boundary layer by small scale disturbances associated with individual pores
Undoing the effect of loss on quantum entanglement
Entanglement distillation is a process via which the strength and purity of
quantum entanglement can be increased probabilistically. It is a key step in
many quantum communication and computation protocols. In particular,
entanglement distillation is a necessary component of the quantum repeater, a
device which counters the degradation of entanglement that inevitably occurs
due to losses in a communication line. Here we report an experiment on
distilling the Einstein-Podolsky-Rosen (EPR) state of light, the workhorse of
continuous-variable entanglement, using the technique of noiseless
amplification. In contrast to previous implementations, the entanglement
enhancement factor achievable by our technique is not fundamentally limited and
permits recovering an EPR state with a macroscopic level of entanglement no
matter how low the initial entanglement or how high the loss may be. In
particular, we recover the original level of entanglement after one of the EPR
modes has passed through a channel with a loss factor of 20. The level of
entanglement in our distilled state is higher than that achievable by direct
transmission of any state through a similar loss channel. This is a key
bench-marking step towards the realization of a practical continuous-variable
quantum repeater and other CV quantum protocols.Comment: 8 pages, 5 figure
Reading-out the state of a flux qubit by Josephson transmission line solitons
We describe the read-out process of the state of a Josephson flux qubit via
solitons in Josephson transmission lines (JTL) as they are in use in the
standard rapid single flux quantum (RSFQ) technology. We consider the situation
where the information about the state of the qubit is stored in the time delay
of the soliton. We analyze dissipative underdamped JTLs, take into account
their jitter, and provide estimates of the measuring time and efficiency of the
measurement for relevant experimental parameters.Comment: 13 pages, 12 figure
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